Spatial pattern of plutonium and radiocaesium contamination released during the Fukushima Daiichi nuclear power plant disaster

Abstract

Plutonium and radiocaesium are hazardous contaminants released by the Fukushima Daiichi nuclear power plant (FDNPP) disaster and their distribution in the environment requires careful characterisation using isotopic information. Comprehensive spatial survey of 134Cs and 137Cs has been conducted on a regular basis since the accident, but the dataset for 135Cs/137Cs atom ratios and trace isotopic analysis of Pu remains limited because of analytical challenges. We have developed a combined chemical procedure to separate Pu and Cs for isotopic analysis of environmental samples from contaminated catchments. Ultra-trace analyses reveal a FDNPP Pu signature in environmental samples, some from further afield than previously reported. For two samples, we attribute the dominant source of Pu to Reactor Unit 3. We review the mechanisms responsible for an emergent spatial pattern in 134,135Cs/137Cs in areas northwest (high 134Cs/137Cs, low 135Cs/137Cs) and southwest (low 134Cs/137Cs, high 135Cs/137Cs) of FDNPP. Several samples exhibit consistent 134,135Cs/137Cs values that are significantly different from those deposited on plant specimens collected in previous works. A complex spatial pattern of Pu and Cs isotopic signature is apparent. To confidently attribute the sources of mixed fallout material, future studies must focus on analysis of individual FDNPP-derived particles.

First determination of Pu isotopes (239Pu, 240Pu and 241Pu) in radioactive particles derived from Fukushima Daiichi Nuclear Power Plant accident

“…(0.335 ± 0.004–0.365 ± 0.015) 23 , and in vegetable reported by Dunne et al . (0.324 ± 0.015 – 0.359 ± 0.07) 25 showed relatively high values among them. It was inferred that these samples were less contaminated by the global fallout source of Pu due to the extremely low transfer factor of global fallout Pu from soil to plant 47 .…”

“…However, due to the relatively large error in the measured values, we cannot distinguish the source unit of the radioactive particles only from these atom ratios. The obtained 240 Pu/ 239 Pu and 241 Pu/ 239 Pu atom ratios in the radioactive particle were also compared with those of various environmental samples, such as soil 21,22 , litter 21,23 , black substance 23 , vegetation 24,25 , river water 26 , and air dust 27 , as shown in Figs 4 and 5. The 240 Pu/ 239 Pu atom ratio detected in environmental samples ranged from 0.14 to 0.381.…”

“…Thus, radioactive particle samples are completely free from the influence of the global fallout and the 240 Pu/ 239 Pu and 241 Pu/ 239 Pu atom ratio reflect the ratio in the core of the FDNPP directly. Therefore, both atom ratio of radioactive particles could provide us more accurate information on the ratio in the core of the FDNPP than other environmental samples and has great potential for source identification of the released radioactive particles in the environment, which should be further explored in a future study.

Figure 4Comparison of atom ratios of 240 Pu/ 239 Pu in various environmental samples, radioactive particles, and source terms: global fallout 15 , soils during 1966–1977 in Japan 16 , soil after the FDNPP accident 21,22 , litter 21,23 , black substance 23 , vegetation 24,25 , river water 26 , average of air dusts 27 , and calculated result of reactor core 28 .

Figure 5Comparison of atom ratios of 241 Pu/ 239 Pu in various environmental samples, radioactive particles, and source terms: global fallout 15 , soil and litter after the FDNPP accident 21 , and calculated result of reactor core 28 .

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“…Comparison of atom ratios of 240 Pu/ 239 Pu in various environmental samples, radioactive particles, and source terms: global fallout 15 , soils during 1966–1977 in Japan 16 , soil after the FDNPP accident 21,22 , litter 21,23 , black substance 23 , vegetation 24,25 , river water 26 , average of air dusts 27 , and calculated result of reactor core 28 .…”

Measurements and modeling of airborne plutonium in Subarctic Finland between 1965 and 2011

“…Previously, an increased 238 Pu/ 239+240 Pu activity ratio due to the SNAP-9A accident has been found in lichens both in Subarctic Finland (Jaakkola et al, 1978) and Sweden (Holm and Persson, 1975) a couple of years after 1964. This delay of over 2 years after the accident indicates the slowness of the interhemispheric transport of stratospheric radionuclides (Fabian et al, 1968). The activity ratio of 238 Pu/ 239+240 Pu cannot be determined for the period immediately after the Chernobyl accident because the activity concentrations of 238 Pu and 239+240 Pu were below the detection limit in April-December 1986.…”